Bottom Line:
There was no effect of the H6N1 LPAIV challenge at 7 weeks of age on the subsequent responses to ND and IBD vaccine at 11 weeks of age, but, surprisingly, the H6N1 LPAIV challenge significantly affected antibody levels to IB vaccine in some breeds, since IB0 and IB14 antibody titers were lower in the challenge groups.However, there was no significant difference in IB28 antibody titers among the experimental groups.The negative effect of the H6N1 LPAIV challenge on IB vaccine response may be related to the fact that both viruses target the lung tissues, and the type of local immune response induced by LPAIV challenge may not be favourable for birds to make optimum IB-specific antibody response.

Background: H6N1 low pathogenic avian influenza virus (LPAIV) are frequently isolated in Taiwan and lead to significant economic losses, either directly or indirectly through association with other infectious diseases. This study investigates immune responses to three different vaccines following a H6N1 challenge in different local breeds.

Methods: Experimental animals were sampled from six local chicken breeds maintained at the National Chung-Hsing University, namely Hsin-Yi, Ju-Chi, Hua-Tung (Taiwan), Quemoy (Quemoy Island), Shek-Ki (China), Nagoya (Japan) and a specific pathogen free (SPF) White Leghorn line. A total number of 338 chickens have been distributed between a control and a challenge group, H6N1 challenge was performed at 7 weeks of age; vaccination against Newcastle Disease (ND), Infectious Bursal Disease (IBD) and Infectious Bronchitis (IB) was performed at 11 weeks. The anti-H6N1 LPAIV antibody titers were measured by ELISA at days 0, 7, 14 and 21 after challenge, and the anti-ND, anti-IBD and anti-IB antibody titers were measured by inhibition of hemagglutination test and ELISA at days 0, 14, 28 after vaccination.

Results: There was no effect of the H6N1 LPAIV challenge at 7 weeks of age on the subsequent responses to ND and IBD vaccine at 11 weeks of age, but, surprisingly, the H6N1 LPAIV challenge significantly affected antibody levels to IB vaccine in some breeds, since IB0 and IB14 antibody titers were lower in the challenge groups. However, there was no significant difference in IB28 antibody titers among the experimental groups.

Conclusions: Local breeds have different immune response to H6N1 LPAIV challenge and subsequent vaccines. Differences dealt mainly with kinetics of response and with peak values. Quemoy exhibited higher antibody levels to H6N1, ND and IBD. The negative effect of the H6N1 LPAIV challenge on IB vaccine response may be related to the fact that both viruses target the lung tissues, and the type of local immune response induced by LPAIV challenge may not be favourable for birds to make optimum IB-specific antibody response.

Figure 4: Antibody titers against IB on 0, 14 and 28 days post-inoculation. a,b within days post-inoculation with no common superscript differ significantly (P < 0.05).

Mentions:
In contrast with the results observed for ND and IBD, the kinetics of antibody titers of IB was modified by the H6N1 LPAIV challenge (Fig 4). Interactions between breed and treatment, as well as between breed and sex, were significant for IB0. Antibody titers at day 0 were lower in the challenge group than in the control group for Ju-Chi and SPF, but did not differ between groups for the other breeds (Fig 5). The effects of breed and H6N1 challenge, without any interaction, were still observed at day 14 post-inoculation. Higher antibody levels were found in the control group for all breeds. Nagoya was the only one to exhibit a stronger response to IB vaccine in the H6N1 control group at day 14, as measured by the difference between titers at day 14 and day 0 (Table 2). The interaction between breed and sex was still significant at day 14 but was not observed at day 28. Breed and treatment effects were significant at day 28; antibody titers became higher in the challenge groups than in the control groups, whatever the breed. The increase in antibody titers between day 14 and day 28 was always higher in the challenge groups as compared to the control groups, this difference was highly significant in Ju-Chi and Nagoya (Table 2) and tended to be significant (P < 0.05) in all other breeds except Shek-Ki which never showed any difference in anti-IB titers between the challenged and the control groups.

Figure 4: Antibody titers against IB on 0, 14 and 28 days post-inoculation. a,b within days post-inoculation with no common superscript differ significantly (P < 0.05).

Mentions:
In contrast with the results observed for ND and IBD, the kinetics of antibody titers of IB was modified by the H6N1 LPAIV challenge (Fig 4). Interactions between breed and treatment, as well as between breed and sex, were significant for IB0. Antibody titers at day 0 were lower in the challenge group than in the control group for Ju-Chi and SPF, but did not differ between groups for the other breeds (Fig 5). The effects of breed and H6N1 challenge, without any interaction, were still observed at day 14 post-inoculation. Higher antibody levels were found in the control group for all breeds. Nagoya was the only one to exhibit a stronger response to IB vaccine in the H6N1 control group at day 14, as measured by the difference between titers at day 14 and day 0 (Table 2). The interaction between breed and sex was still significant at day 14 but was not observed at day 28. Breed and treatment effects were significant at day 28; antibody titers became higher in the challenge groups than in the control groups, whatever the breed. The increase in antibody titers between day 14 and day 28 was always higher in the challenge groups as compared to the control groups, this difference was highly significant in Ju-Chi and Nagoya (Table 2) and tended to be significant (P < 0.05) in all other breeds except Shek-Ki which never showed any difference in anti-IB titers between the challenged and the control groups.

Bottom Line:
There was no effect of the H6N1 LPAIV challenge at 7 weeks of age on the subsequent responses to ND and IBD vaccine at 11 weeks of age, but, surprisingly, the H6N1 LPAIV challenge significantly affected antibody levels to IB vaccine in some breeds, since IB0 and IB14 antibody titers were lower in the challenge groups.However, there was no significant difference in IB28 antibody titers among the experimental groups.The negative effect of the H6N1 LPAIV challenge on IB vaccine response may be related to the fact that both viruses target the lung tissues, and the type of local immune response induced by LPAIV challenge may not be favourable for birds to make optimum IB-specific antibody response.

Background: H6N1 low pathogenic avian influenza virus (LPAIV) are frequently isolated in Taiwan and lead to significant economic losses, either directly or indirectly through association with other infectious diseases. This study investigates immune responses to three different vaccines following a H6N1 challenge in different local breeds.

Methods: Experimental animals were sampled from six local chicken breeds maintained at the National Chung-Hsing University, namely Hsin-Yi, Ju-Chi, Hua-Tung (Taiwan), Quemoy (Quemoy Island), Shek-Ki (China), Nagoya (Japan) and a specific pathogen free (SPF) White Leghorn line. A total number of 338 chickens have been distributed between a control and a challenge group, H6N1 challenge was performed at 7 weeks of age; vaccination against Newcastle Disease (ND), Infectious Bursal Disease (IBD) and Infectious Bronchitis (IB) was performed at 11 weeks. The anti-H6N1 LPAIV antibody titers were measured by ELISA at days 0, 7, 14 and 21 after challenge, and the anti-ND, anti-IBD and anti-IB antibody titers were measured by inhibition of hemagglutination test and ELISA at days 0, 14, 28 after vaccination.

Results: There was no effect of the H6N1 LPAIV challenge at 7 weeks of age on the subsequent responses to ND and IBD vaccine at 11 weeks of age, but, surprisingly, the H6N1 LPAIV challenge significantly affected antibody levels to IB vaccine in some breeds, since IB0 and IB14 antibody titers were lower in the challenge groups. However, there was no significant difference in IB28 antibody titers among the experimental groups.

Conclusions: Local breeds have different immune response to H6N1 LPAIV challenge and subsequent vaccines. Differences dealt mainly with kinetics of response and with peak values. Quemoy exhibited higher antibody levels to H6N1, ND and IBD. The negative effect of the H6N1 LPAIV challenge on IB vaccine response may be related to the fact that both viruses target the lung tissues, and the type of local immune response induced by LPAIV challenge may not be favourable for birds to make optimum IB-specific antibody response.